Fiber optic systems are now in common use for transmitting optical communication signals i.e., optical signals modulated to encode desired information. Such communication signals are used to transmit data, voice and video signals. The optical communication signals are transmitted across a network using optical fibers that support substantial transmission capacity with compact fiber bundles. Given the ever-increasing demands for improved signal quality and bandwidth, it is anticipated that the use of fiber optic communications will continue to increase for years to come.
One of the reasons that fiber optic networks have attracted attention in recent years relates to switching advantages. Because the communication signals in fiber optic networks are optical in nature, conventional electronic switching components can be eliminated. Instead, fiber optic communications lines are connected at a switch by carefully aligning the fiber ends of the lines to be connected for direct optical linkage. Such switching has proved advantageous in that switching can be accomplished quickly without unacceptable signal degradation. However, it will be appreciated that there is a continuing desire to increase the speed of operation and reduce signal losses at switch interfaces.
Controlling switch operation involves target identification and alignment. Target identification refers to identifying two optical fibers that are to be optically interconnected across a switch interface in order to permit subsequent transmission of communication signals therebetween. In this regard, the optical switch may be understood as including a first array of fibers on a first side of the switch and a second array of fibers on a second side of the switch. In reality, the first side fibers and second side fibers may be interspersed in a single chassis structure facing a mirror, or the first and second side fibers may be positioned in a side-by-side arrangement on the same spatial side of a switch interface for optical interconnection via a mirror. It will thus be appreciated that the "first side" and "second side" relate to a signal transmission pathway and not to a spatial arrangement. Thus, target identification may involve identifying one of the first side fibers and one of the second side fibers that are to be interconnected. An optical pathway can then be configured to optically interconnect the identified fibers. Alignment refers to fine tuning the optical connection between the identified fibers to optimize signal transmission.
Heretofore, target identification has involved the use of optical control signals associated with the first and second side fibers. For example, LEDs or other radiation emitting devices may be interspersed with the fibers in the first and second matrices, thereby defining corresponding matrices of LEDs. Identifying a target fiber within a fiber matrix can then be accomplished by lighting the LEDs of the various rows and columns of the LED matrix in a particular pattern to identify the position of the fiber that is to be targeted for connection.
Such targeting methods have certain limitations. First, particularly in the case of large switches, e.g., 256.times.256 fiber lines, a long sequence of pulses may be required for target identification. As a result, the speed of operation of the switch may be reduced. In addition, the need for controlled, sequenced pulsing of the LED arrays generally requires that the LEDs operate by reference to a common system clock. Such central timing entails a singular point where a failure may cripple the whole switch. Accordingly, conventional targeting systems can be slow and unreliable, particularly in the case of large switches.